Method and apparatus for providing communication service to mobile station by multiple base stations in cooperation in wireless communication system

ABSTRACT

A method and an apparatus for providing a service to a Mobile Station (MS) by a plurality of Base Stations (BSs) operating in cooperation in a wireless communication system are provided. The method includes configuring, by a master BS, a first cooperative cell including at least one slave BS, sending a resource request message for requesting resource allocation to the at least one slave BS included in the first cooperative cell, receiving, from each of the at least one slave BS, a resource request response message including resource approval control results for the resource allocation request, changing member BSs constituting the first cooperative cell based on the resource request response message, and allocating resources to an MS that is served in the first cooperative cell.

PRIORITY

This application is a continuation application of a prior applicationSer. No. 13/737,327, filed on Jan. 9, 2013, which claimed the benefitunder 35 U.S.C. §119(a) of a Korean patent application filed on Jan. 9,2012 in the Korean Intellectual Property Office and assigned Serial No.10-2012-0002379, and a Korean patent application filed on May 11, 2012in the Korean Intellectual Property Office and assigned Serial No.10-2012-0050477, the entire disclosure of each of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for providing acommunication service to a Mobile Station (MS) by a plurality of BaseStations (BSs) in cooperation in a wireless communication system.

2. Description of the Related Art

A MS included in a wireless communication system may have a virtual cellthat is formed flexibly or adaptively depending on the MSs moving path.The virtual cell may be considered to be a kind of cooperative cell thatis formed for cooperative communication between BSs. The cooperativecell may include at least one BS, and if the cooperative cell includestwo or more BSs, the BSs may transmit the same or different data to anMS at the same time or at different times.

For example, in a case where the cooperative cell includes two BSs, oneBS may allocate resources of the cooperative cell, serving as a masterBS, and the other BS may provide a service to an MS in cooperation withthe master BS, serving as a slave BS. Since the cooperative cell isflexibly formed depending on the moving path of the MS, the roles of theBSs are also flexible in the cooperative cell. Specifically, a master BSin a first cooperative cell may be changed to another BS, and the masterBS in the first cooperative cell formed to provide a service to a firstMS may operate as a slave BS in a second cooperative cell formed toprovide a service to a second MS.

In the case where one BS simultaneously belongs to several differentcooperative cells in this way, there is a need for a resource allocationscheme for efficiently allocating resources of each BS. The resourceallocation scheme may be classified as a centralized control scheme inwhich a master BS of each cooperative cell allocates resources of allBSs in the cooperative cell, and a distributed control scheme in whicheach BS of each cooperative cell allocates its resources individually.

However, in the centralized control scheme, in a case where a BSsimultaneously belongs to multiple cooperative cells, if a resourceallocation command received from a master BS of each cooperative cellinstructs allocation of the same resources in a duplicate manner,resource allocation conflicts may occur. In this case, if a master BS ofeach cooperative cell coordinates the resource allocations throughsignaling with other BSs in order to prevent the resource allocationconflicts, significant overhead and time delay may occur.

In addition, the distributed control scheme may not be efficient inimproving the system yield through the original inter-cell cooperationof the cooperative cells. Therefore, there is a need for a resourceallocation scheme capable of more efficiently allocating resources ofcooperative cells.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of exemplary embodiments of the present invention are address atleast the above-mentioned problems and/or disadvantages and provide atleast the advantages described below. Accordingly, an aspect of thepresent invention is to provide a method and apparatus for configuringand/or reconfiguring a cooperative cell to provide a communicationservice to one Mobile Station (MS) by multiple Base Stations (BSs) incooperation in a wireless communication system.

Another aspect of the present invention is to provide a method andapparatus for determining a master BS and a slave BS to provide acommunication service in a cooperative cell-based wireless communicationsystem.

Furthermore, another aspect of the present invention is to provide acooperative method and apparatus for efficient resource allocationbetween a master BS and a slave BS in a cooperative cell-based wirelesscommunication system.

In accordance with an aspect of the present invention, a method forproviding a service to a MS by a plurality of BSs operating incooperation in a wireless communication system is provided. The methodincludes configuring, by a master BS, a first cooperative cell includingat least one slave BS; sending a resource request message for requestingresource allocation to the at least one slave BS included in the firstcooperative cell, receiving, from each of the at least one slave BS, aresource request response message including resource approval controlresults for the resource allocation request, changing member BSsconstituting the first cooperative cell according to the resourcerequest response message, and allocating resources to an MS that isserved in the first cooperative cell.

In accordance with another aspect of the present invention, a BaseStation (BS) apparatus for providing a service to a Mobile Station (MS)by a plurality of BSs operating in cooperation in a wirelesscommunication system is provided. The BS apparatus includes a controllerfor configuring, by a master BS, a first cooperative cell including atleast one slave BS, for changing member BSs included in the firstcooperative cell according to a resource request response message whichis received from each of the at least one slave BS belonging to thefirst cooperative cell and which includes resource approval controlresults for a resource allocation request, and for allocating resourcesto an MS that is served in the first cooperative cell, a transmitter forsending a resource request message for requesting resource allocation tothe slave BSs belonging to the first cooperative cell, and a receiverfor receiving the resource request response message from each of the atleast one slave BS that have received the resource request message.

In accordance with further another aspect of the present invention, amethod for providing a service to a Mobile Station (MS) by a pluralityof Base Stations (BSs) operating in cooperation in a wirelesscommunication system is provided. The method includes configuring, by amaster BS, a first cooperative cell including at least one slave BS,sending, to at least one slave BS, upon determining to change the masterBS of the first cooperative cell, a master BS request message forrequesting to make a change to the master BS, receiving, from any one ofthe at least one slave BS, an ACKnowledgement (ACK) indicating apossibility of becoming a master BS, determining a slave BS, from anyone of the at least one slave BS, that has sent the ACK to be a newmaster BS of the first cooperative cell, sending a master BS changemessage indicating the determined new master BS to the MS and all slaveBSs of the first cooperative cell, and providing, by the determined newmaster BS, a service to the MS in cooperation with the at least oneslave BS.

In accordance with yet another aspect of the present invention, a BaseStation (BS) apparatus for providing a service to a Mobile Station (MS)by a plurality of BSs operating in cooperation in a wirelesscommunication system is provided. The BS apparatus includes a controllerfor configuring by a master BS a first cooperative cell including atleast one slave BS, for determining a slave BS that has sent anACKnowledgement (ACK) indicating a possibility of becoming a master BSto be a new master BS of the first cooperative cell, and for controllingthe determined new master BS to provide a service to the MS incooperation with the at least one slave BS, a transmitter for, if thecontroller determines to change the master BS of the first cooperativecell, sending a master BS request message for requesting to make achange to a master BS to the at least one slave BS, and for sending amaster BS change message indicating the determined new master BS to theMS and all of slave BSs of the first cooperative cell, and a receiverfor receiving the ACK from one of the at least one slave BS.

In accordance with still another aspect of the present invention, amethod for providing a service to a Mobile Station (MS) by a pluralityof Base Stations (BSs) operating in cooperation in a wirelesscommunication system is provided. The method includes configuring, bymaster BSs, a resource allocation-cooperative cell and sharinginformation used for resource allocation allocating resourcesconsidering MSs of all BSs belonging to the resourceallocation-cooperative cell in order to optimize performance of thesystem, exchanging information about the resource allocation between BSsbelonging to the resource allocation-cooperative cell, resolving aconflict between resource allocations which may occur during theresource allocation, and providing a service to the MS using theconflict-resolved new resource allocation information.

In accordance with still another aspect of the present invention, a BaseStation (BS) apparatus for providing a service to a Mobile Station (MS)by a plurality of BSs operating in cooperation in a wirelesscommunication system is provided. The BS apparatus includes a controllerfor configuring, by master BSs, a resource allocation-cooperative cell,for sharing information used for resource allocation, for allocatingresources considering MSs of all BSs belonging to the resourceallocation-cooperative cell to optimize performance of the system, andfor resolving a conflict between resource allocations, which may occurduring the resource allocation, and a transmitter for transmittinginformation about the resource allocation to BSs belonging to theresource allocation-cooperative cell, and for providing a service to theMS using the conflict-resolved new resource allocation information.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a procedure for configuring a cloud cell in acommunication system according to a first embodiment of the presentinvention;

FIG. 2 illustrates a procedure for reconfiguring a cloud cell in acommunication system according to a second embodiment of the presentinvention;

FIG. 3 illustrates a procedure for changing a master Base Station (BS)in a cloud cell-based communication system according to a thirdembodiment of the present invention;

FIG. 4 illustrates a procedure for changing a master BS in a cloudcell-based communication system according to a fourth embodiment of thepresent invention;

FIG. 5 illustrates a process of configuring and reconfiguring a cloudcell by a BS in a communication system according to an exemplaryembodiment of the present invention;

FIG. 6 illustrates a process of changing a master BS in a cloudcell-based communication system according to an exemplary embodiment ofthe present invention;

FIG. 7 illustrates a procedure for allocating, by a master BS, resourcesto MSs that set the master BS itself as a master BS in a distributedcontrol scheme according to an exemplary embodiment of the presentinvention;

FIG. 8 illustrates a BS apparatus for performing an operation ofconfiguring and/or reconfiguring a cloud cell and an operation ofchanging a master BS in a cloud cell in a communication system in whichmultiple BSs provide a service to one MS according to an exemplaryembodiment of the present invention; and

FIG. 9 illustrates a Mobile Station (MS) apparatus for performing anoperation of receiving a service provided from multiple BSs by an MSaccording to an exemplary embodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the present invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions are omitted for clarity and conciseness.

Exemplary embodiments of the present invention provide a method andapparatus for providing a communication service to one Mobile Station(MS) by a plurality of Base Stations (BSs) in a cell in which multipleBSs transmit the same or different data to one MS at the same time or atdifferent times. In other words, exemplary embodiments of the presentinvention provide a cooperative cell formed for cooperativecommunication between BSs. The cooperative cell may also be referred toherein as a cloud cell.

FIG. 1 illustrates a procedure for configuring a cloud cell in acommunication system according to a first embodiment of the presentinvention.

Referring to FIG. 1, the communication system includes an MS 100, afirst BS 102, a second BS 104, a third BS 106 and a fourth BS 108.

The MS 100 performs a network entry operation to one of its neighborBSs, for example, to the first BS 102 in step 110, and then the first BS102 operates as a master BS in step 112. The first BS 102 operating asthe master BS sends a measurement indication message to the MS 100 instep 114 to instruct the MS 100 to measure channels of its neighbor BSs,and the MS 100 measures channels of the first to fourth BSs 102 to 108in step 122, and transmits the measurement results to the current masterBS or the first BS 102 using a measurement report message in step 124.The measurement report message may be sent periodically, or may be sentintermittently by a command from a master BS.

Upon receiving the measurement report message, the first BS 102determines members, such as member BSs, that will constitute a cloudcell among the neighbor BSs, based on channel states of the neighborBSs, which are included in the measurement report message, in step 126.The first BS 102 determines or selects members that will constitute acloud cell from among the BSs having an excellent channel stateaccording to certain criteria. The first BS 102 determines the BS havingthe most excellent channel state from among the determined cloud cellmembers as a master BS, and determines the other BSs as slave BSs. Theterm ‘master BS’ as used herein may refer to a BS that allocatesresources of the cloud cell, and the term ‘slave BS’ as used herein mayrefer to a BS providing a service to an MS in cooperation with themaster BS.

In steps 128 and 130, the first BS 102 sends a cloud cell invitationmessage for inviting a BS to become or to serve as a member of the cloudcell to each of the BSs corresponding to the cloud cell membersdetermined in step 126. The cloud cell invitation message includesinformation indicating that each of the second and third BSs 104 and 106receiving the message is invited to become a master BS or a slave BS ofthe cloud cell.

Upon receiving the cloud cell invitation message, the second and thirdBSs 104 and 106 each determine whether to accept the invitation tobecome the cloud cell member through approval control in steps 132 and134. Thereafter, the second and third BSs 104 and 106 transmit thedetermination results to the first BS 102 using a cloud cell invitationresponse message in steps 136 and 138. In the case of an ACKnowledgement(ACK) for accepting the invitation to become a cloud cell member, the BSsends an indicator indicating the invitation acceptance using a cloudcell invitation response message, and in the case of aNegative-ACKnowledgement (NACK) for not accepting or rejecting theinvitation to become a cloud cell member, the BS sends an indicatorindicating the invitation denial using a cloud cell invitation responsemessage.

When sending the NACK, the BS may indicate a reason for rejecting theinvitation, or in other words, a reason for the NACK. The reason for theNACK may include a cell load of the invited BS, an amount of availableresources, the number of other cloud cells to which the BS alreadybelongs, and any other similar and/or suitable reason. Specifically, theBS may reject the invitation to become a cloud cell member if at leastone of: (i) the cell load of the invited BS is high, (ii) the amount ofresources available for a new MS is small because of the high usage ofresources preoccupied for MSs, and (iii) the number of other cloud cellsto which the BS already belongs is greater than a predetermined number.

In steps 140, 142, and 144, the first BS 102 transmits configurationinformation including a list of a master BS and at least one slave BS ofthe cloud cell and information about an MS to which it will provide aservice, to the MS 100 and the members, such as the second and third BSs104 and 106, based on the cloud cell invitation response messages.

Upon receiving the configuration information from the first BS 102, theBSs operate as a master BS or a slave BS depending on the configurationinformation. For example, the first BS 102 operates as a first slave BSin step 146, the second BS 104 operates as a master BS in step 148, andthe third BS 106 operates as a second slave BS in step 150. Therefore,the cloud cell consists of the second BS 104 serving as a master BS, andthe first and third BSs 102 and 106 serving as slave BSs.

FIG. 2 illustrates a procedure for reconfiguring a cloud cell in acommunication system according to a second embodiment of the presentinvention.

Although a cloud cell consisting of a master BS 202, a first slave BS204 and second slave BS 206 will be considered in FIG. 2 by way ofexample, the present invention is not limited thereto, and the cloudcell may consist of one master BS and one or more slave BSs.

In steps 210 and 212, the master BS 202 sends a resource request messagefor requesting resource allocation to the first and second slave BSs 204and 206 at every scheduling cycle. The master BS 202 may send a resourcerequest message to the first and second slave BSs 204 and 206 at anytime, even though the time of sending the resource request message isnot at a predetermined scheduling cycle. The resource request messageincludes information on a required amount of resources, and a type oftraffic in service such as real-time traffic, non-real-time traffic,etc. In a case where the type of traffic in service is real-timetraffic, the resource request message may additionally includeinformation on a maximum allowable delay time, which may also bereferred to as ‘maximum delay time’.

Upon receiving the resource request message, the first and second slaveBSs 204 and 206 perform resource approval control in order to determinewhether to approve the resource allocation request in steps 214 and 216,respectively. The first and second slave BSs 204 and 206 allocateresources in response first to the request for the traffic, a type ofwhich is real-time traffic. If there is a plurality of requests forreal-time traffic, the slave BS allocates resources in response first tothe request, the maximum delay time of which is short. If the maximumdelay time is the same, resources are allocated first to a slave BSoperating as a master BS in another cloud cell among the first andsecond slave BSs 204 and 206.

Thereafter, in steps 217 and 218, the first and second slave BSs 204 and206 each send a resource request response message including the resourceapproval results to the master BS 202 in response to the resourcerequest message.

The resource request response message is sent as an ACK message if anamount of resources allocated is the same as that as requested by themaster BS 202, and the resource request response message is sent as aNACK message if resources cannot be allocated for the amount requestedby the master BS 202. The NACK message may include only the informationindicating the rejection of the resource allocation, and may alsoinclude an amount of resources allocatable, starting from a resourceblock #0, that the master BS 202 can allocate for an MS 200, and areason to reject resource allocation. Examples of the reason to rejectresource allocation may be any of the following: (1) a traffic priorityof another cloud cell, to which the first and second slave BSs 204 and206 belong, is higher; (2) the maximum delay time of another cloud cell,to which the first and second slave BSs 204 and 206 belong, is shorter;and (3) the first and second slave BSs 204 and 206 each are a master BSin other cloud cells, to which the first and second slave BSs 204 and206 belong. However, the present invention is not limited thereto, andthe rejection reason may be any suitable reason.

It will be assumed in the present exemplary embodiment of FIG. 2 thatthe first slave BS 204 has approved the resource allocation request fromthe master BS 202, and the second slave BS 206 has rejected the resourceallocation request from the master BS 202.

In step 220, the master BS 202 may reconfigure the cloud cell based onthe resource approval results included in the resource request responsemessage. Specifically, the master BS 202 determines at least one slaveBS that will participate in the communication, and determines at leastone slave BS that it will exclude from the cloud cell members. In FIG.2, the first slave BS 204 that has approved the resource allocationrequest may be determined as a slave BS that will participate in thecooperative communication with the master BS 202, and the second slaveBS 206 may be determined as a slave BS that will be excluded from thecloud cell members if the second slave BS 206 has sent a NACK message inresponse to the resource allocation request a predetermined number oftimes or more.

Thereafter, the master BS 202 sends a resource allocation message, whichindicates its intention to use resources, to the first slave BS 204determined to participate in the cooperative communication, in step 224,and sends a cloud cell information message including informationindicating exclusion of the second slave BS 206 from the cloud cell tothe second slave BS 206 determined to be excluded from the cloud cellmembers in step 226. In step 222, the master BS 202 sends a cloud cellresource allocation message indicating from which BSs the entireresources of the cloud cell are allocated, to the MS 200. Although it isassumed in FIG. 2 that the master BS 202 sends a resource allocationmessage indicating its intention to use resources to the first slave BS204, it will be apparent to those of ordinary skill in the art that themaster BS 202 may send the resource allocation message indicating itsintention not to use resources depending on its decision. As the masterBS 202 uses resources of the first slave BS 204 in this way, the masterBS 202 and the first slave BS 204 may transmit data to the MS 200 incooperation in steps 228 and 230, respectively.

The master BS 202 may serve as a slave BS in another cloud cell, andbelow-described steps 232 to 236 will be assumed to be a case where themaster BS 202 operates as a slave BS in another cloud cell. The masterBS 202 receives a resource request message for requesting resourceallocation from a master BS of another cloud cell, i.e., a third BS 208,in step 232, performs resource approval control in step 234, and sends aresource request response message including the resource approvalcontrol results to the third BS 208 in step 236.

As discussed above, the procedure for configuring a cloud cell, andtransmitting data by a slave BS, which is a member of the cloud cell, incooperation with the master BS through resource approval control, hasbeen described by way of example with reference to FIGS. 1 and 2. Aprocedure for changing a master BS while the master BS and a slave BSare transmitting data in cooperation will be described below.

FIG. 3 illustrates a procedure for changing a master BS in a cloudcell-based communication system according to a third embodiment of thepresent invention.

Referring to FIG. 3, the communication system includes an MS 300, amaster BS 302, a first slave BS 304 and a second slave BS 306. Themaster BS 302, the first slave BS 304 and the second slave BS 306constitute a first cloud cell, and the first and second slave BSs 302and 304 are assumed to be members of a second cloud cell.

In step 310, the master BS 302 of the first cloud cell determines tochange a master BS of the first cloud cell if it cannot provide theminimum service quality or minimum Quality of Service (QoS) to the MS300 or if its channel state is less than a threshold for a predeterminedtime. The channel state information may be acquired from a measurementreport message received, for example, from the MS 300 or from any othersuitable source.

Upon determining to change the master BS, the master BS 302 the sends amaster BS request message for requesting to become a master BS to eachof the first and second slave BSs 304 and 306, which are members of thefirst cloud cells, in steps 312 and 314. The master BS request messageincludes a type of traffic, such as real-time traffic or non-real-timetraffic, that the master BS 302 serves, and the required minimum amountof resources. If the traffic that the master BS 302 serves is real-timetraffic, then the master BS request message may also include the maximumdelay time. The first and second slave BSs 304 and 306, to which themaster BS 302 sends the master BS request message, may be BSs whosechannel quality is greater than or equal to a threshold.

Upon receiving the master BS request message, the first and second slaveBSs 304 and 306 determine whether they can provide the minimum servicequality to the MS 300, or determine priorities of the master BS of thesecond cloud cell, which is another cloud cell to which they belong, andthe master BS 302 of the first cloud cell, through master BS approvalcontrol in steps 316 and 318, respectively, and send an ACK message or aNACK message to the master BS 302 in response to the master BS requestmessage depending on the consideration results, in steps 320 and 322,respectively. Based on the master BS request message, the slave BSs 304and 306 each allocate resources depending on the resource allocationpriority, determine whether they can support the required minimum amountof resources requested in the master BS request message, and send an ACKmessage if they can support the required minimum amount of resources.

The slave BS allocates resources in response to the request for thetraffic, a type of which is real-time traffic. If there is a pluralityof requests for real-time traffic, the slave BS allocates resources inresponse to the request, the maximum delay time of which is short. Ifthe maximum delay time is the same, resources are allocated to a slaveBS operating as a master BS in another cloud cell from among the firstand second slave BSs 304 and 306.

If the slave BS sends a NACK message because it cannot support therequired amount of resources requested in the master BS request message,then the slave BS may include the following rejection reasons in theNACK message. Examples of the rejection reason may be at least one ofthe following: (1) a traffic priority of another cloud cell, to whichthe first and second slave BSs 304 and 306 belong, is higher; (2) themaximum delay time of another cloud cell, to which the first and secondslave BSs 304 and 306 belong, is shorter; and (3) the first and secondslave BSs 304 and 306 each are a master BS in other cloud cells, towhich the first and second slave BSs 304 and 306 belong. However, thepresent invention is not limited thereto, and the rejection reason maybe any suitable reason.

It will be assumed in the exemplary embodiment of FIG. 3 that the firstslave BS 304 sends an ACK message in step 320 and the second slave BS306 sends a NACK message in step 322. The master BS 302 determines thefirst slave BS 304 that sent an ACK message, as a new master BS in step324, and sends a master BS change message including informationindicating the change of the master BS to a new master BS, to each ofthe first and second slave BSs 304 and 306 and the MS 300 in steps 326,328 and 330. Although not shown, the master BS 302 may determine the newmaster BS and also at least one new slave BS in step 324.

Thereafter, the first slave BS 304 that the master BS 302 determined asa new master BS operates as a master BS in the first cloud cell in step334 upon receiving the master BS change message in step 326, the masterBS 302 operates as a first slave BS in step 322, and the second slave BS306 operates as a second slave BS in step 336 upon receiving the masterBS change message in step 328.

Although it is assumed in the exemplary embodiment of FIG. 3 that an ACKis received from only the first slave BS 304 by way of example, the ACKmay be received from two or more slave BSs, and if an ACK is receivedfrom each of two or more slave BSs, the master BS 302 may consider theother channel state and cell load, and determine one slave BS having alower cell load as a new master BS if their channel states are better orthe same.

If a NACK is received from both of the first and second slave BSs 304and 306, then the master BS 302 compares rejection reasons receivedtogether with the NACK, selects one slave BS, a priority of whoserejection reason is lower, and determines the selected slave BS as a newmaster BS of the first cloud cell. An operation of determining a newmaster BS upon receiving a NACK from both of the first and second slaveBSs 304 and 306 will be described below in more detail.

FIG. 4 illustrates a procedure for changing a master BS in a cloudcell-based communication system according to a fourth embodiment of thepresent invention.

Referring to FIG. 4, the communication system includes a first MS 400, afirst BS 402, a second BS 404, a third BS 406, a fourth BS 408, and afifth BS 410. In addition, the communication system is assumed toinclude a first cloud cell and a second cloud cell. The first cloud cellincludes the MS 400, the first BS 402 operating as a master BS, and thesecond and third BSs 404 and 406 operating as slave BSs. The secondcloud cell includes a second MS (not shown), the second BS 404 operatingas a slave BS, and the fifth BS 410 operating as a master BS.Specifically, in the present exemplary embodiment of FIG. 4, the secondBS 404 is assumed to be a BS that is included in both the first andsecond cloud cells.

If the first BS 402 operating as a master BS receives a NACK messageindicating the rejection of becoming a master BS from the second andthird BSs 404 and 406 operating as slave BSs in step 420, then the firstBS 402 selects one slave BS by comparing rejection reasons receivedtogether with the NACK message, and determines the selected slave BS asa new master BS in step 422.

Upon receiving a NACK message from each of the second and third BSs 404and 406, the first BS 402 then sends a master BS push message to a BSthat sent rejection reason (1), if there is a BS that sent rejectionreason (1) from among the rejection reasons included in the NACKmessages received by the first BS 402. If there is a plurality of BSsthat sent rejection reason (1), then the first BS 402 selects a BShaving the best channel state from among the BSs, and sends the masterBS push message to the selected BS. If the channel states are the same,a BS having a low cell load is selected, and if the cell loads are alsothe same, a BS is selected at random.

If there is only a BS that sent rejection reason (2) from among therejection reasons included in the received NACK messages, then the firstBS 402 sends a master BS push message to the BS that sent rejectionreason (2). If there is a plurality of BSs that sent rejection reason(2), then the first BS 402 selects a BS having the best channel statefrom among the BSs, and sends the master BS push message to the selectedBS. If the channel states are the same, a BS having a low cell load isselected, and if the cell loads are also the same, a BS is selected atrandom.

If there is only a BS that sent rejection reason (3) from among therejection reasons included in the received NACK messages, then the firstBS 402 sends a measurement indication message to the first MS 400 tofind another nearby BS in step 424, without sending the master BS pushmessage. Specifically, the first BS 402 sends, to the first MS 400, themeasurement indication message for commanding to find a new BS bymeasuring channels of its neighbor BSs, and sends a master BS pushmessage for pushing to become a new master BS, to the second BS 404 instep 426.

Upon receiving the master BS push message, the second BS 404 sends anACK message for approving the push for the master BS to first BS 402 instep 430, operating as a master BS of the first cloud cell, and sends amaster BS change message indicating its change to a master BS of thefirst cloud cell to the fifth BS 410, which is a master BS of anothercloud cell, i.e., the second cloud cell, to which it belongs, in step428.

Upon receiving the master BS change message, the fifth BS 410 adjustsresource allocation of the second cloud cell, which is changed as thesecond BS 404 becomes a master BS of the first cloud cell, in step 434,and transmits the adjustment results to the second BS 404 using aresource allocation message in step 436.

The first BS 402 sends a master BS change message to the second andthird BSs 404 and 406 and the first MS 400 in steps 438, 440 and 442,the master BS change message, which includes information indicating thatthe master BS of the first cloud cell is changed to the second BS 404 asthe first BS 402 determines the second BS 404 as a new master BS in step422.

Having received the measurement indication message, the first MS 400measures channels of the first BS 402 and the second to fourth BSs 404to 408 in step 432, and transmits the measurement results to the currentmaster BS, i.e., the second BS 404, using a measurement report messagein step 444. The measurement report message may be sent periodically, ormay be sent sporadically by a command from a master BS.

Thereafter, if the second BS 404 does not provide the minimum servicequality to the first MS 400 or if its channel state is less than athreshold for a predetermined time, then the second BS 404 determines tochange the master BS of the first cloud cell in step 446, and determinesthe fourth BS 408 having the most excellent channel state as a master BSbased on the channel states of neighbor BSs, which are included in themeasurement report message received from the first MS 400.

Thereafter, in step 448, the second BS 404 sends a master BS requestmessage for requesting to become a master BS of the first cloud cell tothe fourth BS 408 determined as a candidate for the master BS, in step448. Upon receiving the master BS request message, the fourth BS 408determines whether it can provide the minimum service quality to thefirst MS 400 through the master BS approval control in step 450, andsends an ACK message for accepting the master BS request message to thesecond BS 404 in step 452 if it can provide the minimum service qualityto the first MS 400. Thereafter, in steps 454 to 460, the second BS 404sends a master BS change message, indicating the change of the master BSof the first cloud cell from the second BS 404 to the fourth BS 408, toeach of the first BS 402, the first MS 400, the third BS 406, and thefourth BS 408.

FIG. 5 illustrates a process of configuring and reconfiguring a cloudcell by a BS in a communication system according to an exemplaryembodiment of the present invention.

Referring to FIG. 5, in step 501, the BS operating and referred to as amaster BS sends, to an MS, a measurement indication message forinstructing to measure channel states of its neighbor BSs. In step 503,the master BS receives, from the MS, a measurement report messageincluding channel measurement results for the neighbor BSs.

In step 505, the master BS configures a cloud cell consisting of BSshaving an excellent channel state, for example, BSs whose channel stateis greater than or equal to a threshold, based on the receivedmeasurement report message. In step 507, the master BS sends a messageincluding configuration information of the cloud cell configured in step505, to all of the cloud cell members, i.e., slave BSs, and the MS.

If it is determined in step 509 that a predetermined scheduling cyclehas come or that the master BS needs additional resources in addition tothe resources allocated thereto, the master BS sends a resource requestmessage for requesting resource allocation to the slave BSs constitutingthe cloud cell in step 511. In step 513, the master BS receives, fromthe slave BSs, a resource request response message including approvalcontrol results for determining whether to approve or accept theresource allocation request.

In step 515, the master BS determines at least one slave BS to beincluded in and at least one slave BS to be excluded from the cloud cellto be reconfigured during reconfiguration of the cloud cell depending onthe approval control results, and reconfigures the cloud cell dependingon the determination results. For reconfiguration of the cloud cell, themaster BS may additionally consider the measurement report message thatis periodically received from the MS. Specifically, the master BSdetermines to include a slave BS that can provide the requestedresources to the MS for a threshold time or more, during reconfigurationof the cloud cell, and determines to exclude a slave BS that does notprovide the requested resource to the MS for the threshold time or more,during reconfiguration of the cloud cell.

In step 517, the master BS sends a resource allocation messageindicating its intention to use resources to the slave BS determined tobe included during reconfiguration of the cloud cell, and sends a cloudcell information message including information indicating its exclusionfrom the cloud cell to the slave BS determined to be excluded duringreconfiguration of the cloud cell. In addition, the master BS sends tothe MS a cloud cell resource allocation message indicating from whichBSs the entire resources of the cloud cell are allocated.

FIG. 6 illustrates a process of changing a master BS in a cloudcell-based communication system according to an exemplary embodiment ofthe present invention.

Referring to FIG. 6, in step 601, the master BS determines to change amaster BS of a first cloud cell if it does not provide the minimumservice quality or if its channel state is less than a threshold for apredetermined time or more. In step 603, the master BS sends a master BSrequest message for requesting to become a master BS to each of slaveBSs constituting the first cloud cell.

In step 605, the master BS determines whether a response message, suchas an ACK/NACK message, indicating the possibility of becoming a masterBS is received from the slave BSs. The master BS proceeds to step 607upon receiving an ACK message from any one of the slave BSs, andproceeds to step 613 upon receiving a NACK message.

First, upon receiving an ACK message from any one of the slave BSs instep 607, the master BS determines a slave BS that sent the ACK messageto be a new master BS of the first cloud cell in step 609, and sends amaster BS change message, which indicates the change of the master BS tothe determined new master BS, to the slave BSs constituting the firstcloud cell and the MS, in step 611.

Although it is assumed in the exemplary embodiment of FIG. 6 that theACK is received from one slave BS by way of example, the presentinvention is not limited thereto, and the ACK may be received from atleast two slave BSs or from any other suitable source. If the ACK isreceived from the at least two slave BSs, then the master BS determinesone slave BS, that is selected based on the other channel state and cellload, to be a new master BS.

Next, upon receiving a NACK message from any one of the slave BSs instep 613, the master BS compares rejection reasons received togetherwith the NACK messages, selects one slave BS having a rejection reasonwhose priority is lower, and determines the selected slave BS as a newmaster BS, in step 615.

In step 617, the master BS sends a push message for the determined newmaster BS to be a master BS to the new master BS determined in step 615.In step 619, the master BS determines whether an ACK message forapproving the push for the new master BS is received. Upon receiving theACK message, the master BS sends a master BS change message indicatingthe change of the master BS to the determined new master BS, to theslave BSs constituting the first cloud cell and the MS, in step 611.However, upon failure to receive the ACK message in step 619, the masterBS returns to step 615.

Although not shown, if the new master BS, as determined in step 615, isincluded in the first cloud cell and also in another cloud cell, i.e., asecond cloud cell, then the BS determined as the new master BS sends amaster BS change message, which indicates its change to the master BS ofthe first cloud cell, to a master BS of the second cloud cell, andreceives, from the master BS of the second cloud cell, a resourceallocation message including results on the resource allocation which isadjusted as the new master BS is included in the second cloud cell.

FIG. 7 illustrates a procedure for allocating, by a master BS, resourcesto MSs that set the master BS itself as a master BS in a distributedcontrol scheme according to an exemplary embodiment of the presentinvention.

A cloud cell for each MS is configured in accordance with the proceduresdescribed with reference to FIGS. 1 and 2 and other procedures of theexemplary embodiments of the present invention. Each MS may receive datafrom a master BS or slave BSs, and resource allocation for each MS maybe determined by the master BS. Multiple BSs constitute a resourceallocation-cooperative cell. The resource allocation-cooperative cell isa cell configured with respect to one master BS, unlike the cooperativecell that is configured with respect to an MS. Specifically, theresource allocation-cooperative cell is formed with respect to aspecific master BS, and may include another master BS or slave BS of anMS that sets the specific master BS as its master BS or slave BS.

The distributed control scheme-based resource allocation procedure isachieved in the following four steps.

1) Information Sharing Step

In an information sharing step 701, all information needed to allocateresources to each MS in a scheduling assignment step 703 is sharedbetween BSs in the resource allocation-cooperative cell. Particularly,the information shared in the information sharing step 701 includesinformation, such as Channel State Information (CSI), interfering linkinformation, and any other similar and/or suitable information, used tocalculate a specific metric that is used to allocate resources to MSs inthe scheduling assignment step 703. The CSI may include information forindicating the channel state and quality between each MS and each BSbelonging to the MS's cloud cell. The interfering link information mayinclude index information of a BS in which the amount of interferencethat each MS suffers is greater than or equal to a threshold.

2) Scheduling Assignment Step

In the scheduling assignment step 703, each master BS allocates theresources to MSs of all BSs in the resource allocation-cooperative cellusing the information shared in the information sharing step 701, anddetermines the resources it will allocate to the MSs belonging to themaster MS. Each master BS allocates resources to MSs so as to maximize aspecific metric, such as a sum of average data rates of BSs and a sum oftransmit powers of BSs, in which fairness between MSs is considered,which is calculated considering all BSs in the resourceallocation-cooperative cell. The master BS selects one or some MSs fromamong MSs of all BSs in the resource allocation-cooperative cell, as atarget for resource allocation depending on the amount of its availableresources. The MSs may be selected in accordance with Equation (1)below.

$\begin{matrix}{U^{*} = {\arg\;{\max\limits_{U}{\prod\limits_{U \Subset {\{{k❘{k \in {M_{j}\mspace{14mu}{for}\mspace{14mu} j} \in S_{i}}}\}}}\;\left( {1 + \frac{R_{k}}{\left( {T - 1} \right)R_{k}^{\prime}}} \right)}}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

Equation (1) is used for selecting MSs for resource allocation in ani-th BS, which may be a master BS. Equation (1) is used to find a set U*of MSs, from among all the MSs that set BSs in the resourceallocation-cooperative cell as its master BS or slave BSs, wherein theset U* is of MSs that maximize a specific metric. A value obtained bymultiplying all (1+R_(k)/((T−1)*R_(k)′) with respect to MSs belonging tothe set is used as an example of the specific metric.

In Equation (1), R_(k) denotes a data rate, i.e., a throughput, at whichdata can be transmitted to a k-th MS when resources are allocatedpresently, and R_(k)′ denotes an average data rate, i.e., an averagedata rate of a k-th MS until the previous time slot, for a k-th MS untilresources are allocated. T denotes a window size used to calculate anaverage data rate, i.e., denotes a time or interval in which an averageis taken to calculate an average data rate. S_(i) denotes a set of BSs,including an i-th BS as well, in the resource allocation-cooperativecell configured centering on the i-th BS, and M_(j) denotes a set of MSsthat have a j-th BS as their master BS.

3) Information Exchange Step

In an information exchange step 705, the scheduling assignment resultsand additional information needed in the next step, i.e., a conflictresolution step 706, are exchanged between BSs in the resourceallocation-cooperative cell. The scheduling assignment results exchangedbetween BSs are resource allocation information for the MSs belonging toa master BS in the set U* that the master BS selected using Equation(1). However, resource allocation information for all the MSs belongingto the set U* may be exchanged to assist in the conflict resolution step706 or the re-scheduling assignment step. The addition informationincludes priority information for allocation of each resource. Thepriority information represents importance of each allocation withrespect to the system performance. As an example, a value of(1+R_(k)/((T−1)*R_(k)′) in Equation (1) may be used as priorityinformation of resource allocation for a k-th MS. As another example, areciprocal of the minimum delay time value of the service that the MSreceives may be used as priority information.

4) Conflict Resolution Step

Conflicts may occur between resources allocated by different BSs.Specifically, if the same resources are allocated to different MSs, itmay be a case where conflicts have occurred between two resourceallocations.

In the conflict resolution step 706, conflicts are resolved inaccordance with predefined rules in a BS having the same resources,between which conflicts have occurred. For example, priorityinformation, which may be acquired in the information exchange step 705,for two resource allocations, between which conflicts have occurred, maybe compared to invalidate the low-priority resource allocation. Newresource allocation information obtained after the resolution ofconflicts is delivered to master BSs of MSs related to the conflicts.

After the conflict resolution step 706, each BS transmits data to the MSaccording to the conflict resolving new resource allocation information.If the BS is a master BS, then it may re-allocate the secured resourcesto other MSs. The scheduling assignment step 703, the informationexchange step 705 and the conflict resolution step 706 may be repeatedlyperformed, and after the repetition is completed, each BS may transmitdata to the MS according to the information about resources allocated inthe scheduling assignment step 703 or according to new resourceallocation information in the conflict resolution step 706.

FIG. 8 illustrates a BS apparatus for performing an operation ofconfiguring and/or reconfiguring a cloud cell and an operation ofchanging a master BS in a cloud cell in a communication system in whichmultiple BSs provide a service to one MS according to an exemplaryembodiment of the present invention.

According to the present exemplary embodiment, the BS apparatus in FIG.8 may perform an operation of allocating, by a master BS, resources toMSs that set the master BS as their master BS as shown in the exemplaryembodiment of FIG. 7. However, the present invention is not limitedthereto, and the BS apparatus of FIG. 8 may perform other suitableoperations of a BS apparatus.

Referring to FIG. 8, the BS includes a transmitter 800, a receiver 810and a controller 820.

First, a description will be made of the operation of configuring andreconfiguring a cloud cell by a BS. If the transmitter 800 sends ameasurement indication message for instructing to measure channels ofits neighbor BSs to an MS and the receiver 810 receives, from the MS, ameasurement report message including the channel measurement results,the controller 820 may configure a first cloud cell consisting of BSswhose channel state is greater than or equal to a threshold, based onthe received measurement report message, and may control the transmitter800 to transmit member information of the first cloud cell to each ofthe slave BSs constituting the first cloud cell and the MS.

If the master BS needs additional resources in addition to the resourcesallocated thereto, the controller 820 may control the transmitter 800 tosend a resource request message for requesting resource allocation toslave BSs constituting the first cloud cell, and may control thereceiver 810 to receive a resource request response message includingapproval control results for determining whether to approve the resourceallocation request, from each of the slave BSs. Thereafter, thecontroller 820 may reconfigure the first cloud cell according to theapproval control results.

Next, a description will be made of the operation of changing a masterBS in a cloud cell by a BS. The controller 820 may configure a firstcloud cell, including one master BS and at least one slave BS asdescribed above, and if the controller 820 determines to change themaster BS of the first cloud cell, the controller 820 may control thetransmitter 800 to send a master BS request message for requesting tobecome a master BS to each of the at least one slave BS, and may controlthe receiver 810 to receive an ACK message indicating the possibility ofbecoming a master BS from any one of the at least one slave BS.

Thereafter, the controller 820 may determine a slave BS that sent theACK to be a new master BS of the first cloud cell, and may control thetransmitter 800 to send a master BS change message indicating thedetermined new master BS to the MS and each of the at least one slaveBS. Upon receiving a NACK and a corresponding rejection reason from eachof at least two slave BSs through the receiver 810, the controller 820may compare the received rejection reasons, determine a slave BS havinga lower-priority rejection reason as a new master BS, and control thetransmitter 800 to send a push message for the determined new master BSto become a master BS to the determined new master BS.

FIG. 9 illustrates an MS apparatus for performing an operation ofreceiving a service provided from multiple BSs by an MS according to anexemplary embodiment of the present invention.

According to the present exemplary embodiment, the MS apparatus in FIG.9 may be an MS to which a master BS has allocated resources inallocating resources to MSs that set the master BS as their master BS asshown in the exemplary embodiment of FIG. 7. However, the presentinvention is not limited thereto, and the MS apparatus of the presentexemplary embodiment may be an MS having resources allocated accordingto any suitable manner.

Referring to FIG. 9, the MS includes a transmitter 900, a receiver 910and a controller 920. If the receiver 910 receives a measurementindication message for instructing the MS to measure channels of itsneighbor BSs from a master BS included in a first cloud cell, then thecontroller 920 controls the transmitter 900 to send a measurement reportmessage including channel measurement results for the neighbor BSs.After the receiver 910 receives information about the members includedin the first cloud cell consisting of the master BS and at least oneslave BS from the master BS, then the controller 920 receives a servicethat the master BS and the at least one slave BS provide in cooperation.

Upon detecting the change of the master BS from a BS of the first cloudcell to a new master BS, the controller 920 controls the receiver 910 toreceive a master BS change message, which indicates the BS determined asthe new master BS, from the master BS. As is apparent from the foregoingdescription, the exemplary embodiments of the present invention providea method of providing a communication service to one MS by multiple BSsin cooperation in a wireless communication system, making it possible tomore efficiently use the limited resources and thus contributing to theimprovement of the service quality level provided to MSs.

In addition, according to the exemplary embodiments of the presentinvention, a BS that simultaneously belongs to several differentcooperative cells in the centralized control scheme or the distributedcontrol scheme may prevent conflicts which may occur as resourceallocation commands received from master BSs of different cooperativecells allocate the same resources in a duplicate manner.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for receiving a service from a pluralityof base stations (BSs) by a mobile station (MS) in a wirelesscommunication system, the method comprising: receiving a measurementindication message instructing to measure channels of neighbor BSs froma master BS of a cooperative cell including the master BS allocatingresources of the cooperative cell and at least one slave BS providing aservice to the MS in cooperation with the master BS; transmitting ameasurement report message including measurement results of the channelsof the neighbor BSs; receiving configuration information related to thecooperative cell from the master BS; and receiving a service providedbased on the master BS and the at least one slave BS in cooperation. 2.The method of claim 1, further comprising: receiving a master BS changemessage indicating that the master BS is changed to a new master BS fromthe master BS, if the master BS of the first cooperative is changed tothe new master BS.
 3. The method of claim 1, further comprising:receiving resource allocation information related to a conflict-resolvedresource which resolves a conflict between resource allocationsoccurring in a resource allocation procedure of resourceallocation-cooperative cells, wherein the service is received based onthe resource allocation information.
 4. The method of claim 3, whereinthe MS is selected based on the following equation, as one among MSs ofall BSs of each of the resource allocation-cooperative cells,$U^{*} = {\arg\;{\max\limits_{U}{\prod\limits_{U \Subset {\{{k❘{k \in {M_{j}\mspace{14mu}{for}\mspace{14mu} j} \in S_{i}}}\}}}\;\left( {1 + \frac{R_{k}}{\left( {T - 1} \right)R_{k}^{\prime}}} \right)}}}$where Rk denotes a data rate at which data is transmitted to a k-th MSwhen resources are allocated presently, Rk' denotes an average data ratefor a k-th MS until resources are allocated, T denotes a window sizeused to calculate the average data rate, S_(i) denotes a set of BSs in aresource allocation-cooperative cell configured with respect to an i-thBS, and M_(j), denotes a set of MSs having a j-th BS as the master BS.5. A mobile station (MS) for receiving a service from a plurality ofbase stations (BSs) in a wireless communication system, the MScomprising: a receiver configured: to receive a measurement indicationmessage instructing to measure channels of neighbor BSs from a master BSof a cooperative cell including the master BS allocating resources ofthe cooperative cell and at least one slave BS providing a service tothe MS in cooperation with the master BS, to receive configurationinformation related to the cooperative cell from the master BS, and toreceive a service provided based on the master BS and the at least oneslave BS in cooperation, and a transmitter configured to transmit ameasurement report message including measurement results of the channelsof the neighbor BSs.
 6. The MS of claim 5, wherein the receiver isfurther configured to receive a master BS change message indicating thatthe master BS is changed to a new master BS from the master BS, if themaster BS of the cooperative cell is changed to the new master BS. 7.The MS of claim 5, wherein the receiver is further configured to receiveresource allocation information related to a conflict-resolved resourcewhich resolves a conflict between resource allocations occurring in aresource allocation procedure of resource allocation-cooperative cells,and wherein the service is received based on the resource allocationinformation.
 8. The MS of claim 7, wherein the MS is selected based onthe following equation, as one among MSs of all BSs of each of theresource allocation-cooperative cells,$U^{*} = {\arg\;{\max\limits_{U}{\prod\limits_{U \Subset {\{{k❘{k \in {M_{j}\mspace{14mu}{for}\mspace{14mu} j} \in S_{i}}}\}}}\;\left( {1 + \frac{R_{k}}{\left( {T - 1} \right)R_{k}^{\prime}}} \right)}}}$where R_(k) denotes a data rate at which data is transmitted to a k-thMS when resources are allocated presently, R_(k)′ denotes an averagedata rate for a k-th MS until resources are allocated, T denotes awindow size used to calculate the average data rate, Si denotes a set ofBSs in a resource allocation-cooperative cell configured with respect toan i-th BS, and M_(j), denotes a set of MSs having a j-th BS as themaster BS.